Re: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim

[Christoph Hellwig]

On Wed, Jun 16, 2010 at 09:17:55AM +0900, KAMEZAWA Hiroyuki wrote:
> yes. It's only called from 
> 	- page fault
> 	- add_to_page_cache()
> 
> I think we'll see no stack problem. Now, memcg doesn't wakeup kswapd for
> reclaiming memory, it needs direct writeback.

The page fault code should be fine, but add_to_page_cache can be called
with quite deep stacks.  Two examples are grab_cache_page_write_begin
which already was part of one of the stack overflows mentioned in this
thread, or find_or_create_page which can be called via
_xfs_buf_lookup_pages, which can be called from under the whole XFS
allocator, or via grow_dev_page which might have a similarly deep
stack for users of the normal buffer cache.  Although for the
find_or_create_page we usually should not have __GFP_FS set in the
gfp_mask.

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